1. Field of the Invention
The invention is related to the field of wafer fabrication and, in particular, to fabricating wafer structures with aerodynamic shapes so that the structures are less likely to be damaged during cleaning processes.
2. Statement of the Problem
Wafer fabrication is a procedure composed of many repeated sequential processes of depositing layers of material, and patterning the deposited layers to produce structures for electrical circuits, devices, chips, etc. For example, wafer fabrication is typically used to build semiconductor components, such as amplifiers, transistors, and MEMS devices. Wafer fabrication is also used to build magnetic recording or magnetic memory devices, such as magnetoresistance (MR) read elements, write elements, etc. Some of the processes commonly used in wafer fabrication are photolithography, nanoimprint lithography, etc.
Photolithography is a process used to selectively remove parts of a thin film. As an example of photolithography, a wafer is covered with photoresist. An exposure system then shines ultraviolet light through a photomask to produce an image on the photoresist. The ultraviolet light changes the chemistry of the exposed photoresist, which allows a solution, referred to as a “developer”, to remove the exposed photoresist. The result is a photoresist on the wafer having a desired pattern. The pattern in the photoresist is then used to pattern one or more layers on the wafer to form the desired structures. For instance, a milling process may be used to remove any material that is exposed by the photoresist to form structures underneath the photoresist. In another instance, a material may be plated or deposited on areas of the wafer that are exposed by the photoresist to form the structures. After the structures are formed, the photoresist is removed.
Subsequent to wafer fabrication processes forming structures, a cleaning process may be performed to remove residual particles which remain on the structures due to surface tension, re-deposition, etc. If the residual particles are not removed by the cleaning process, then the particles may cause problems in subsequent processing steps or in the final product.
In one common cleaning process, a high-velocity fluid flow, such as carbon dioxide in a supercritical state, is directed onto the surface of the wafer. As the fluid flow passes over the wafer, the flow removes residual particles from the surfaces that are exposed to the flow. The fluid flow is typically directed onto the surface of the wafer from multiple angles or is swept between multiple angles. For instance, assume that a structure has a square or rectangular shape. To remove residual particles from each side of the structure, the flow should be directed towards the structure from all four sides. Also, the structures may have indentations or pockets where residual materials are trapped. Directing the fluid flow from multiple angles helps to remove these residual materials from the indentations or pockets.
In present wafer fabrication, the structures being built are getting smaller and smaller, such as on the nanometer scale. One problem encountered is that the small structures tend to be fragile and the cleaning processes may damage the structures on the wafer. To avoid damaging the structures, the velocity of the flow may be reduced, or the flow may be directed along the wafer's minimum cross section. This unfortunately reduces the effectiveness of the cleaning process.
It is therefore desirable to develop wafer fabrication techniques that generate small structures on a wafer, but also facilitate cleaning processes performed on the wafer.